Encapsulate QQmlContextData

This class is not a private detail of QQmlContext. And it is incredibly
hard to see who owns what in there. Let's add some civilization ...

We enforce refcounting for QQmlContextData across the code base, with
two exceptions:

1. QQmlContextPrivate may or may not own its QQmlContextData.
2. We may request a QQmlContextData owned by its parent QQmlContextData.

For these two cases we keep flags in QQmlContextData and when the
respective field (m_parent or m_publicContext) is reset, we release()
once.

Furthermore, QQmlContextData and QQmlGuardedContextData are moved to
their own files, in order to de-spaghettify qqmlcontext_p.h and
qqmlcontext.cpp.

When the QQmlEngine is deleted, any QQmlComponents drop their object
creators now, in order to release any context data held by those.
Before, the context data would be deleted, but the object creators would
retain the dangling pointer.

[ChangeLog][QML][Important Behavior Changes] QQmlContext::baseUrl() does
what the documentation says now: It prefers explicitly set baseUrls over
compilation unit URLs. Only if no baseUrl is set, the CU's URL is
returned. It used to prefer the CU's URL.

Change-Id: Ieeb5dcb07b45d891526191321386d5443b8f5738
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

3 files changed, 26 insertions, 29 deletions

diff --git a/src/qmlmodels/qqmldelegatemodel.cpp b/src/qmlmodels/qqmldelegatemodel.cpp
index 08c91d172e..710cc359b4 100644
--- a/src/qmlmodels/qqmldelegatemodel.cpp
+++ b/src/qmlmodels/qqmldelegatemodel.cpp
@@ -267,7 +267,6 @@ QQmlDelegateModel::~QQmlDelegateModel()
 
             cacheItem->object = nullptr;
             cacheItem->contextData->invalidate();
-            Q_ASSERT(cacheItem->contextData->refCount == 1);
             cacheItem->contextData = nullptr;
             cacheItem->scriptRef -= 1;
         }
@@ -957,10 +956,8 @@ void QQDMIncubationTask::initializeRequiredProperties(QQmlDelegateModelItem *mod
     if (incubatorPriv->hadRequiredProperties()) {
         QQmlData *d = QQmlData::get(object);
         auto contextData = d ? d->context : nullptr;
-        if (contextData) {
-            contextData->hasExtraObject = true;
-            contextData->extraObject = modelItemToIncubate;
-        }
+        if (contextData)
+            contextData->setExtraObject(modelItemToIncubate);
 
         if (incubatorPriv->requiredProperties().empty())
             return;
@@ -1022,9 +1019,9 @@ void QQDMIncubationTask::initializeRequiredProperties(QQmlDelegateModelItem *mod
             }
         }
     } else {
-        modelItemToIncubate->contextData->contextObject = modelItemToIncubate;
+        modelItemToIncubate->contextData->setContextObject(modelItemToIncubate);
         if (proxiedObject)
-            proxyContext->contextObject = proxiedObject;
+            proxyContext->setContextObject(proxiedObject);
     }
 }
 
@@ -1039,7 +1036,7 @@ void QQDMIncubationTask::statusChanged(Status status)
         incubating->object = nullptr;
         if (incubating->contextData) {
             incubating->contextData->invalidate();
-            Q_ASSERT(incubating->contextData->refCount == 1);
+            Q_ASSERT(incubating->contextData->refCount() == 1);
             incubating->contextData = nullptr;
         }
         incubating->scriptRef = 0;
@@ -1174,7 +1171,7 @@ void QQmlDelegateModelPrivate::incubatorStatusChanged(QQDMIncubationTask *incuba
         cacheItem->scriptRef -= 1;
         if (cacheItem->contextData) {
             cacheItem->contextData->invalidate();
-            Q_ASSERT(cacheItem->contextData->refCount == 1);
+            Q_ASSERT(cacheItem->contextData->refCount() == 1);
         }
         cacheItem->contextData = nullptr;
 
@@ -1269,15 +1266,14 @@ QObject *QQmlDelegateModelPrivate::object(Compositor::Group group, int index, QQ
         for (int i = 1; i < m_groupCount; ++i)
             cacheItem->incubationTask->index[i] = it.index[i];
 
-        QQmlContextData *ctxt = new QQmlContextData;
-        ctxt->setParent(QQmlContextData::get(creationContext  ? creationContext : m_context.data()));
+        QQmlRefPointer<QQmlContextData> ctxt = QQmlContextData::createRefCounted(
+                    QQmlContextData::get(creationContext  ? creationContext : m_context.data()));
         cacheItem->contextData = ctxt;
 
         if (m_adaptorModel.hasProxyObject()) {
             if (QQmlAdaptorModelProxyInterface *proxy
                     = qobject_cast<QQmlAdaptorModelProxyInterface *>(cacheItem)) {
-                ctxt = new QQmlContextData;
-                ctxt->setParent(cacheItem->contextData, /*stronglyReferencedByParent*/true);
+                ctxt = QQmlContextData::createChild(cacheItem->contextData);
                 QObject *proxied = proxy->proxiedObject();
                 cacheItem->incubationTask->proxiedObject = proxied;
                 cacheItem->incubationTask->proxyContext = ctxt;
@@ -2252,9 +2248,10 @@ void QQmlDelegateModelItem::childContextObjectDestroyed(QObject *childContextObj
     if (!contextData)
         return;
 
-    for (QQmlContextData *ctxt = contextData->childContexts; ctxt; ctxt = ctxt->nextChild) {
-        if (ctxt->contextObject == childContextObject)
-            ctxt->contextObject = nullptr;
+    for (QQmlRefPointer<QQmlContextData> ctxt = contextData->childContexts(); ctxt;
+         ctxt = ctxt->nextChild()) {
+        if (ctxt->contextObject() == childContextObject)
+            ctxt->setContextObject(nullptr);
     }
 }
 
@@ -2359,8 +2356,8 @@ void QQmlDelegateModelItem::destroyObject()
     Q_ASSERT(data);
     if (data->ownContext) {
         data->ownContext->clearContext();
-        if (data->ownContext->contextObject == object)
-            data->ownContext->contextObject = nullptr;
+        if (data->ownContext->contextObject() == object)
+            data->ownContext->setContextObject(nullptr);
         data->ownContext = nullptr;
         data->context = nullptr;
     }
@@ -2379,12 +2376,12 @@ void QQmlDelegateModelItem::destroyObject()
 QQmlDelegateModelItem *QQmlDelegateModelItem::dataForObject(QObject *object)
 {
     QQmlData *d = QQmlData::get(object);
-    QQmlContextData *context = d ? d->context : nullptr;
-    if (context && context->hasExtraObject)
-        return qobject_cast<QQmlDelegateModelItem *>(context->extraObject);
-    for (context = context ? context->parent : nullptr; context; context = context->parent) {
+    QQmlRefPointer<QQmlContextData> context = d ? d->context : nullptr;
+    if (QObject *extraObject = context ? context->extraObject() : nullptr)
+        return qobject_cast<QQmlDelegateModelItem *>(extraObject);
+    for (context = context ? context->parent() : nullptr; context; context = context->parent()) {
         if (QQmlDelegateModelItem *cacheItem = qobject_cast<QQmlDelegateModelItem *>(
-                context->contextObject)) {
+                context->contextObject())) {
             return cacheItem;
         }
     }
diff --git a/src/qmlmodels/qqmldelegatemodel_p_p.h b/src/qmlmodels/qqmldelegatemodel_p_p.h
index 8684439508..20fb47f021 100644
--- a/src/qmlmodels/qqmldelegatemodel_p_p.h
+++ b/src/qmlmodels/qqmldelegatemodel_p_p.h
@@ -149,7 +149,7 @@ public:
 
     QV4::ExecutionEngine *v4;
     QQmlRefPointer<QQmlDelegateModelItemMetaType> const metaType;
-    QQmlContextDataRef contextData;
+    QQmlRefPointer<QQmlContextData> contextData;
     QPointer<QObject> object;
     QPointer<QQmlDelegateModelAttached> attached;
     QQDMIncubationTask *incubationTask;
@@ -222,7 +222,7 @@ public:
 
     QQmlDelegateModelItem *incubating = nullptr;
     QQmlDelegateModelPrivate *vdm = nullptr;
-    QQmlContextData *proxyContext = nullptr;
+    QQmlRefPointer<QQmlContextData> proxyContext;
     QPointer<QObject> proxiedObject  = nullptr; // the proxied object might disapear, so we use a QPointer instead of a raw one
     int index[QQmlListCompositor::MaximumGroupCount];
 };
diff --git a/src/qmlmodels/qqmltableinstancemodel.cpp b/src/qmlmodels/qqmltableinstancemodel.cpp
index 8c034356f3..4152cbe3ea 100644
--- a/src/qmlmodels/qqmltableinstancemodel.cpp
+++ b/src/qmlmodels/qqmltableinstancemodel.cpp
@@ -68,7 +68,7 @@ void QQmlTableInstanceModel::deleteModelItemLater(QQmlDelegateModelItem *modelIt
 
     if (modelItem->contextData) {
         modelItem->contextData->invalidate();
-        Q_ASSERT(modelItem->contextData->refCount == 1);
+        Q_ASSERT(modelItem->contextData->refCount() == 1);
         modelItem->contextData = nullptr;
     }
 
@@ -325,10 +325,10 @@ void QQmlTableInstanceModel::incubateModelItem(QQmlDelegateModelItem *modelItem,
     } else {
         modelItem->incubationTask = new QQmlTableInstanceModelIncubationTask(this, modelItem, incubationMode);
 
-        QQmlContextData *ctxt = new QQmlContextData;
         QQmlContext *creationContext = modelItem->delegate->creationContext();
-        ctxt->setParent(QQmlContextData::get(creationContext  ? creationContext : m_qmlContext.data()));
-        ctxt->contextObject = modelItem;
+        QQmlRefPointer<QQmlContextData> ctxt = QQmlContextData::createRefCounted(
+                    QQmlContextData::get(creationContext  ? creationContext : m_qmlContext.data()));
+        ctxt->setContextObject(modelItem);
         modelItem->contextData = ctxt;
 
         QQmlComponentPrivate::get(modelItem->delegate)->incubateObject(